<div class="timer">
  <span class="timer-hour" v-show="showHour">
    {{ hour }}
  </span>
  <span class="timer-separator" v-show="showHour">:</span>
  <span class="timer-minute" v-show="showMinute">
    {{ minuteStr }}
  </span>
  <span class="timer-separator" v-show="showMinute">:</span>
  <span class="timer-second">
    {{ secondStr }}
  </span>
</div>
